1. Field of the Invention
The present invention relates to an automatic sound field correcting system for automatically correcting a sound field characteristic in an audio system having a plurality of loudspeakers.
2. Description of the Related Art
The audio system that is equipped with a plurality of loudspeakers to provide a high quality sound field space is required to produce automatically the proper sound field space that can give a presence. In other words, when the listener tries to get the proper sound field space by himself or herself by operating the audio system, it is extremely hard to properly adjust a phase characteristic, a frequency characteristic, a sound pressure level, etc. of a reproduced sound that is played back via a plurality of loudspeakers. For this reason, it is required to correct automatically the sound field characteristic on the audio system side.
In the prior art, as the audio system of this type, the audio system disclosed in Utility Model Application Publication (KOKAI) Hei 6-13292 has been known. In this audio system in the prior art, an equalizer that receives audio signals on a plurality of channels to adjust these frequency characteristics of respective audio signals and a plurality of delay circuits that delay the audio signals output from the equalizer every channel are provided, and then outputs of respective delay circuits are supplied to a plurality of loudspeakers.
Also, in order to correct the sound field characteristic, there are provided a pink noise generator, an impulse generator, a selector circuit, a microphone used to measure the reproduced sound being reproduced by the loudspeakers, a frequency analyzer, and a delay time calculator. Then, a pink noise generated by the pink noise generator is supplied to the equalizer via the selector circuit, and an impulse signal generated by the impulse generator is directly supplied to the loudspeakers via the selector circuit.
Upon correcting the phase characteristic of the sound field space, propagation delay times of the impulse sound from the loudspeakers to a listening position are measured by measuring the impulse sound reproduced via the loudspeakers by the microphone while supplying directly the impulse signal from the above impulse generator to the loudspeakers and then analyzing the measured signals by using the delay time calculator.
In other words, the propagation delay times of respective impulse sounds are measured by directly supplying the impulse signal to individual loudspeakers while shifting a time and calculating time differences from points of time when respective impulse signals are supplied to respective loudspeakers to points of time when respective impulse sounds being reproduced by every loudspeaker come up to the microphone by using the delay time calculator. Thus, the phase characteristic of the sound field space can be corrected by adjusting the delay times of respective channels of the above delay circuit based on respective measured propagation delay times.
Also, upon correcting the frequency characteristic of the sound field space, the pink noise is supplied from the pink noise generator to the equalizer and then the reproduced sounds of the pink noise being reproduced via a plurality of loudspeakers are measured by the microphone, and then frequency characteristics of these measured signals are analyzed by the frequency analyzer. Thus, the frequency characteristic of the sound field space can be corrected by feedback-controlling the frequency characteristic of the equalizer based on the analyzed results.
In the audio system in the prior art, as described above, in order to correct the frequency characteristic of the sound field space, such a method is employed that the frequency characteristics of the reproduced sounds of the pink noise are analyzed by using a group of narrow-band filters and then the analyzed results are fed back to the equalizer.
Here, upon producing the reproduced sounds of the pink noise, the pink noise is supplied to the equalizer after the frequency characteristic of the equalizer is set to a frequency characteristic which mates with the audio playback. Accordingly, the reproduced sounds of the pink noise being reproduced via a plurality of loudspeakers reach the microphone and then the frequency characteristics of the reproduced sound of the pink noise are analyzed by a group of narrow-band filters.
However, in case the frequency characteristics of measured signals derived from the reproduced sounds of the pink noise being reproduced via a plurality of (all) loudspeakers are frequency-analyzed by individual narrow-band filters in a group of narrow-band filters, the analyzed result suitable for the frequency characteristic of the equalizer cannot be obtained with good precision. As a result, there is such a subject that, if the frequency characteristic of the equalizer is feedback-controlled based on the analyzed result, it becomes difficult to correct properly the frequency characteristic of the sound field space.
In addition, there is such another subject that, since the phase characteristic of the sound field space is corrected based on the delay times that are obtained by supplying directly the impulse signal to the loudspeakers, the phase characteristic of the overall audio system cannot be corrected into the phase characteristic that can produce the proper sound field space.